Research Of Fiber Methane Gas Detection Based On The Principle Of Spectrum Absorption

In recent years, the coal mine accidents , especially gas exploding, happen frequently in china, which has endangered the miners'lives and the safety of the national properties. Methane is the main composition of the gas in the mineral well, So it is very important to detecting methane concentration in mine safety and environment inspecting areas. The fiber gas detection technology carry the signal by the light and transfer signal by the fiber, so it is a high sensitivity gas detection technique. Methane concentration measurement is the paper's purpose. Fiber methane gas sensing technique is studied based on the principle of spectrum absorption.Firstly, kinds of the fiber detecting technologies are introduced in the paper, and the actualities and progress directions of the fiber gas sensor are reviewed at home or abroad. The influence factors and key techniques of fiber gas sensor are analyzed. The basic principle of gas absorption measurement is given through the analysis of molecule spectrum theory. The near-infrared absorption spectrum of methane is chosen. And its absorption characteristic is analyzed. Thus, the basic principle of sensor's mathematical model is given.Secondly, the characteristics and influences on measurement of light source, gas cell, detector, optical path and electric signal detection system are analyzed. The grin lens gas cell is designed which can reduce interference signal. And the principle of lock in amplifier technique is given. Therefore, the weak signal can be picked up and amplified.Finally, we report the investigation into the interference noise caused by the methane system, modulate them by Matlab and indicate that the noises depend on factors such as cell length , amplitude of frequence modulation and so on. Then we can minimize the noise and improve the detection resolution by judicious choice,which is very important for our instruction. To compensate for the methane weak absorption in near-infrared region., high sensitivity harmonic detection techniques are employed. Based on the current experimental device, the characteristics of the source spectrum and the near-infrared absorption of methane are tested. The methane concentration detection, the repeatability and stabilityof the system are studied. The experiments results have proved that the system is feasible.